curl: fix some security problems

curl: fix some security problems

This fixes the following security problems:
* CVE-2017-1000254: FTP PWD response parser out of bounds read
* CVE-2017-1000257: IMAP FETCH response out of bounds read
* CVE-2018-1000005: HTTP/2 trailer out-of-bounds read
* CVE-2018-1000007: HTTP authentication leak in redirects
* CVE-2018-1000120: FTP path trickery leads to NIL byte out of bounds write
* CVE-2018-1000121: LDAP NULL pointer dereference
* CVE-2018-1000122: RTSP RTP buffer over-read
* CVE-2018-1000301: RTSP bad headers buffer over-read

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>